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C. G. SMITH MAGNETIC SPEkDOMETER.

APPLICATION man AUG-$1918- Patented Aug. 5, ME).

UNITED STATES PATENTOFFIOE- CHARLES G. SMITH, OFWASHINGTOIN', DISTRICT COLUMBIA, ASSIGNOB. TO CHARLES l a FISCHER, OF BROOKLYN, NEW YORK.

MAGNETIC srnsnomn'rna To all whom it may concern:

Be it known that I, CHARLES G. S ITH, a citizen of the United States, and a resident of Washington, District of Columbia, have invented certain new and useful Improvements in Magnetic Speedometers, of which I the" following is a specification.

Jill

In my prior Patent 1,207,647 of December 5,1906, I havedescribed a magnetic speedometer characterized by constant intensity of magnetization and consequent uniformity of torque, and in a cop'ending application Serial No. 248,983, 'filed August 8, 1918, I have disclosed certain features of construc tion and relationwhereby this principle is rendered applicable to or may be approximated in speedometers having rotating magpresent applicationsets forth another valunets with eccentric or traveling fields. The

able specific form of the invention generic to the two applicationsa'nd claimed broadly in the other case. In the constructionset forth herein both members of the magnetic circuit rotate, and various other distinctive features are included, as will hereinafter ,appear. In general, the object is to provide another eflicient design adapted to embody the principles set forth in my other specifications.

In the accompanying drawings: Figure 1 is a central vertical section;

Fig. 2 is an enlarged horizontal section The instrumentmay be contained in an;

upright circular case 1, having an ,upper window 2 through which thespeedometer indication is visible, and lower windows 3 behind which odometer indicators 4 may be located. A hub 5 is mounted rotatably upon the upwardly projecting portion of a fixed axle 6 rising from a frame portion 7 within the casing. The bottom of this hub has internal beveled gear teeth 8 meshed by a.

I fipecificationof Letters Patent. Patent d A g. 5; 1919 Application flleaAugust 8, I 1

191a Serial .No. 243,984.

beveled driving pinion 9 on. an inclined shaft 10, which passes through the rear Wall of the casing. i

The rotatin magnet 11 is preferably of a clrcular horses 1oe type, with its poles at one and the same side of the axis of rotation, and 1s sulta'bly'fixed on the hub, which may have a basal flange 12 for the magnet to rest upon. In the particular form illustrated an underframe 13 is interposed between the magnet and flange, all being held rigidly together, and this frame serves as a support for an armature 14 constituting the other member of the magnetic circuit, and which is thus coupled with the magnet to rotate therewith.

and south poles of the magnet, and preferably, also, it hes at'the outer side of the magnet and substantially in its plane. The

armature mayor may not itself be a magnet,

but preferably it is made of soft iron.

O ne or both of the members of the magnetic circuit are provided with series of concentrating teeth 15. It is sufficient, however,

that they be formed on the ends of the armature which are opposed to the polar ends of the magnet. I The central or intermediate part 'ofthe armature is without teeth. For

the reasons enplained in the aforesaid copendmg appllcatlon it is advantageous to laminate the teeth; and in the present case whole being riveted together and to the support.

The space between the armature and magnet 1s for the reception of an oscillatory conducting annulus 18, preferably formed by the dependingfl ange of a cup. This flange is of copper, or of some alloy having a lower this is most conveniently effected by buildtemperature coefficient, and is slotted by vertical slots 19, which extend to the lower edgejofthe flange, where they are electrically open. As explained in my other application, the region bars 20 between the slots p a 65 The armature 14 is preferably short so as merely to overlap the gap between the north.

should be as narrow as practicable, but are materially wider than the slots and preferably about twice as wide as the concen= trating teeth.

The upper part of the cup, above the magnetic field, may be made in a separate piece or crown 21, which need not be of conducting material, and which, not requiring to be slotted, may bear directly on it As illustrated, the indicator crown 21 may be made wider than the slotted conductor flange or annulus 18, so as tooverhang the Furthermore, it is important that t e teeth armature and bring the characters close to the window.

In operation, the eddy currents set up. in the conductor are not dependent upon the strength .of the permanent magnet, and neither is the torque, so long as the magnet is stronger than'a value sufiicient to saturate the teeth 15. This is true if the slots in the conductor are open and if the magnetizing field is substantially uniform over a bar as large or larger than a re ion 20.

be narrower than the regions 20. I It will be -understood, therefore, that eddy currents are produced within each region 20 as a tooth passes it, but the general field does not produce eddy currents, because the slots 19 prevent circulation across them, and these particular currents must pass across or around the slots or not exist. The general magnetic field is composed of all the lines of force emanating from and entering the north and south'poles of the magnet, and since these are much wider than the regions 20, the only effect of the travel of the poles as a whole past the regions is to create a difference ofpotential between the inner and outer portions of the regions, and as the latter are not connected in closed circuitwith each other a resulting current can not pass. Hence the chief currents generated in the conductor are due to the excess magnetism of the teeth 15 over and above the general magnetism. This excess magnetism I shall call MI, following the usual notation;'the general magnetism I shall call H after the customary notation. If now the field H is more than stron enough to saturate the teeth, then I, the intensity of magnetization of the teeth, remains a constant ,tnaximum value. Any increase or decrease of H, due to any change in the strength of the magnet, does not affect I so long as such changes lie in a range above that value of H which saturates the teeth. Consequently the torque is uniform.

What I claim as new is:

1. In a magnetic speedometer, the combi nation of two members of a magnetic circuit coupled and mounted so that both rotate and having poles at one side of the axis of rotation so as to produce a traveling field, one of said members being provided with a series of concentrating teeth, and an oscillatory conductor slotted transversely to the circumferential direction with open slots, the width of the regions or-bars between the slots being greater than that of the teeth, whereby the teeth set up eddy currents within said bars.

2. In a magnetic speedometer, the combi nation of an approximately circular horseshoe magnet, a short armature spaced from and spanning the gap of the magnet, one

of said members being provided in its portions opposed to the other with series of concentrating teeth, means uniting the said members in the stated relation and permitting their rotation, and an interposed oscillatory conductor slotted transversely to the circumferential direction with open slots.

3. In a magnetic speedometer, the combination of a horseshoe magnet, a short armature spaced from the poles of the magnet and provided with a series of concentrating teeth, means couphng and mounting sai members for rotation, and an interposed centrating teeth, means coupling and mounting said members for rotation, and an interposed oscillatory conductor )rovided with open slots transverse to the (irection of movement, the width of the regions or bars between the open slots being greater than that of the teeth.

5. In a magnetic speedometer, the combination of a horseshoe magnet. a short armature spaced from and spanning the gap in the magnet, one of said members being provided on its portions opposed to the other with series of concentrating teeth, and an interposed conductor cup having its flange slotted with open slots.

'6. In a magnetic speedometer, the combination of a horseshoe magnet, a short armature spaced from and spanning the gap in the magnet, one of said members being pro vided on its portions opposed to the other with series of concentrating teeth, means for coupling and rotating both members. and a conductor cup having its interposed flange slotted with open slots and an indicator crown above its slotted portion.

mmmm m '71". In a magmatic speedommw, Mha combi and m condluctmr cup having its interposedl nation of a horsas'hoe magnet, 21. short m'maflange slotted to its edge, Where the slots 1mm spaced hum and spanning the gap in are open, the: regions between the slots bem the magnet, one of said members being proing Wider than the teeth.

5 vided on its portions opposed to the (Whale 111 testimony whereof, have signed my with series of concelltmltin teeth, means name to this specification. for coupling and rotating imth members CHARLES Gr. SMITJHL 

